This material is based upon work supported by Veterans Affairs
Rehabilitation Research and Development Service (C891-RA and RCTR
597-0160).Address all correspondence and requests for reprints to: James A.
Henry, PhD, Rehabilitation Research and Development, National Center for
Rehabilitative Auditory Research, VA Medical Center (NCRAR), PO Box
1034, Portland, OR 97207; email: henryj@ohsu.edu.

Abstract--Clinical assessment of the perceptual
characteristics of tinnitus usually includes an attempt to match the
pitch of tinnitus to a pure tone. A standardized clinical protocol for
tinnitus pitch matching does not yet exist, and there is a history of
unsuccessful attempts to obtain such measures reliably. The present
study was designed to evaluate new protocols for identifying the
perceived pitch of tinnitus, with the objectives of reducing testing
time and improving test-retest reliability. Two protocols ("Octave"
and "Binary") were developed, each of which was patterned after the
testing procedure previously developed at the Oregon Tinnitus Clinic and
used to assess thousands of tinnitus patients. Both protocols use
computer-automation to conduct testing; the protocols differ
according to their specific testing algorithms. Twenty subjects with
non-fluctuating tinnitus were each tested over two sessions. Results of
testing revealed that both protocols could obtain pitch matches within
20 to 25 min. Reliability of responses was good for some subjects but not
others, and the Binary protocol generally provided more reliable
results.

INTRODUCTION

Tinnitus is the perception of sound that does not have an acoustic
source outside of the head. Most people have experienced tinnitus at
least as a transient event. Although prevalence estimates vary, an
average estimate is that 40-50 million Americans have chronic tinnitus.
Of these, 10-12 million seek professional help, and 2.5 million are
debilitated by their tinnitus condition.

Although there are many causes for tinnitus, the most common is
noise-induced hearing loss. Tinnitus is, thus, a common complaint among
veterans. According to VA Central Office, Analysis and Statistics
Service, over 115,000 veterans with service-connected tinnitus receive
over $110,000,000 per year in tinnitus disability compensation. Providing
tinnitus management for veterans is hindered by a lack of standards for
both tinnitus assessment and treatment that could otherwise be adopted
for VA application. Our efforts are directed toward providing such a
standard of care for veterans who have clinically significant tinnitus.

The present study was designed to address the need for clinical
methodology to quantify, accurately and reliably, the phantom sensation
of tinnitus. This need was identified in 1982 by the National Academy of
Sciences (1) who specified several lines of related research that were
"necessary as a basis for establishing a standardized test procedure."
Unfortunately, standardized test procedures have still not been
universally adopted. Recently, Tyler (2) wrote, "The quantification of
a symptom is fundamental to understanding its mechanisms and treatments.
If we can't measure it, we cannot study it." Tyler went on to explain
in detail why it is important to measure tinnitus. The interested reader
is referred to Tyler, as well as other publications addressing the value
of clinical tinnitus assessment (3,4).

At clinics where tinnitus measurement is conducted, there is almost
universally an attempt to determine the tinnitus pitch using some
variation of a tone-matching procedure. Many methods for tinnitus pitch
matching have been reported, but reliability of the measures has
generally been poor (5). In particular, there is a lack of studies
demonstrating reliable pitch matches with a technique that can be used
clinically.

We recently reported a prototype system that performed
computer-automated tinnitus loudness and pitch matching (6). The
pitch-matching method used with the prototype system was patterned after
a method used for over 20 years at the Oregon Tinnitus Clinic. The initial
study with the automated system documented the feasibility of obtaining
reliable tinnitus loudness and pitch matches using computer automation.
However, testing time ranged from 38 to 79 min to obtain a pitch match.
There was, therefore, large variability in how subjects responded to the
uniform testing protocol, and testing time clearly had to be shortened
for this technique to attain clinical utility. The automated procedure
for pitch matching was modified in an effort to shorten testing time
while maintaining optimum response reliability. Two versions of the
modified protocol were designed for the present study: the "Binary"
and "Octave" procedures. Subjects were evaluated over repeated
sessions to determine the test-retest reliability of pitch matches
obtained with these protocols.

METHODS

Subjects
Twenty subjects participated in this study, including 3 females and
17 males, with a mean age of 60.1 y (range, 24-78; SD, 10.6). Subjects
were selected based on having tonal, stable tinnitus, to minimize any
variability in the tinnitus that might confound interpretation of the
reliability analyses. Seven of the subjects had previous
tinnitus-matching experience, and the remaining 13 subjects were naive
to any form of tinnitus assessment. Each subject returned for a second
experimental session within 2 weeks of the first.

Equipment
Subjects were tested in an Acoustic Systems 19701A double-walled
sound booth. The testing equipment has been described in detail (7).
Briefly, there were four major system components: 1) The main computer,
located in the control room, controlled all parameters of testing; 2) A
laptop computer (Compaq Concerto), located in the sound booth, provided
the automated-testing interface between the individual being tested and
the main computer. The notebook computer was enabled for Microsoft
Windows for Pen, allowing the subject to use a pen-pointing device to
indicate responses on a touch-sensitive video screen; 3) A custom-built,
signal-conditioning module was used for signal mixing, attenuation, and
earphone buffering; and, 4) Etymotic Research ER-4B Canal PhoneTM
insert earphones were used for signal transduction. Calibration
procedures for this equipment have also been described previously (7).

ProceduresInitial Evaluation
At the start of the first session, standard audiometric evaluation
was performed, including case history, tympanometry, and measures of
hearing sensitivity at 0.25-8 kHz. Instrumentation and procedures for
the initial evaluation were as described in Fausti et al. (8).

Selection of Test Ear
Matching tinnitus to tones in the contralateral ear is generally
considered to be less challenging for the tinnitus patient than
ipsilateral matching (7,9). Therefore, one ear was chosen as the
"tinnitus ear" for each subject, and the contralateral ear was chosen
as the "test ear." If one ear had more predominant tinnitus, that ear
was chosen as the tinnitus ear. If the subject had symmetrical tinnitus,
the tinnitus ear was chosen randomly.

Experimental Protocols
The entire testing protocol was under computer control, including
instructions for responding, and all testing was repeated at a second
session.

Instructions to Subjects
There were three interleaved response tasks for the testing
protocols: threshold testing, loudness matching, and pitch matching.
Instructions for responding were displayed on the patient's video screen
each time the task changed. The instruction screen for threshold testing
was shown previously (10), as was the instruction screen for tinnitus
loudness matching (7). The instruction screen for pitch matching is
shown in Figure 1a.

Test Frequencies
Available test frequencies for the pitch-matching tasks were in the
range 0.5-16 kHz, each separated by one-third octave. For both
pitch-matching protocols, automated hearing thresholds were obtained,
followed by loudness matching, at each frequency that was used for pitch
matching (not all test frequencies were used for pitch matching).

Common Procedures for Pitch Matching
The basic testing algorithm was designed to replicate closely the
clinical testing protocol for tinnitus pitch matching as described by
Vernon (11). Hearing threshold evaluation, tinnitus loudness matching
and tinnitus pitch matching were sequenced to ensure that pitch-matching
tones were presented only at levels that were previously matched to the
tinnitus loudness. For each of the two pitch match protocols, an
adaptive two-alternative forced choice (2AFC) procedure was used to
determine the frequency of a pure tone that subjects identified as
closest to their perceived tinnitus pitch (11,12). For each tone pair,
tones were presented consecutively for 4 sec each with an inter-tone
interval of 1 sec.

The automated program sequenced through the test frequencies in
order of increasing or decreasing frequency, dependent upon the
responses of the subject. Pitch matching did not occur until thresholds
and loudness matches had been obtained at the first two test
frequencies. At that time, pitch-matching instructions appeared on the
screen (Figure 1a) and the subject selected "Go" when the
instructions were read and understood. The computer screen then showed
that tones were being presented during pitch matching, i.e., "Tone 1"
appeared on the screen during the presentation of the first tone, and
"Tone 2" during the presentation of the second tone. Following
termination of Tone 2, response buttons appeared (Figure 1b).
Subjects were thus required to listen to both tones before making a
response choice.

For the pitch-matching task, the lower frequency tone was presented
first, followed by the higher frequency tone, and the subject was
instructed to choose the tone that was closest to his/her tinnitus
pitch. In general, if the higher frequency tone was chosen, the program
moved to a higher test frequency, while selection of the lower frequency
tone moved the program to a lower frequency.

When the final pitch match had been selected, the computer program
entered a special loop to test for "octave confusion," a common
mistake that tinnitus patients make during pitch matching, described by
Vernon and Fenwick (12). Octave confusion was checked at the frequency
one octave higher than the final pitch-matched frequency, then at the
frequency one octave lower (only if these test frequencies were
available). When the program switched to these octave frequencies, the
threshold and loudness match were obtained (if they had not been
already), and pitch matching occurred using the two frequencies
separated by one octave.

Pre-testing Evaluation to Determine Subjects' Understanding of Pitch
and Loudness
Before testing with the automated system, subjects received
pretesting to confirm their understanding of the concepts of pitch and
loudness, and training regarding these concepts if there was confusion.
The pre-testing protocol is shown in the Appendix.

"Octave" Procedure
The computer algorithms for obtaining sequenced thresholds and
loudness matches have been described previously (7). For the Octave
procedure, thresholds and loudness matches were first obtained at 1 kHz,
then at 1.26 kHz. Pitch matching, using the 2AFC procedure, was then
done using the loudness-matched tones from each of the first two test
frequencies. If the higher frequency tone was chosen as closest in pitch
to the subject's tinnitus, the computer then obtained a threshold and
loudness match at the next higher octave (2 kHz) and at 2.52 kHz. With
each 2AFC selection of the higher of two test frequencies, the computer
went to the next higher octave frequency and repeated this procedure.
The 2AFC selection of the lower frequency of a tone pair indicated that
the pitch match had been bracketed to within the octave below the pair.
At that point, the computer conducted the same protocol through the
bracketed frequency range, from lower to higher frequencies, to
determine a pitch match to the closest one-third octave frequency. This
was followed by octave-confusion testing.

"Binary" Procedure
With the Binary procedure, the computer started testing at 3.18 kHz.
A threshold and loudness match was obtained at 3.18 kHz, followed by a
threshold and loudness match at 4 kHz. Pitch matching, using the 2AFC
procedure, was then done, and the frequency choice determined whether
further testing would occur below 3.18 kHz or above 4 kHz. Thus, the
initial frequency choice resulted in binary bracketing, either to the
lower or to the upper frequency range. Movement to new frequencies was
then in octave steps, and the computer further bracketed the pitch match
to within an octave. When this had been done, testing proceeded as with
the Octave protocol, i.e., through the bracketed-frequency range to
determine the pitch match with a resolution of one-third octave,
followed by octave-confusion testing.

RESULTS

For each of the two procedures, there was one pitch match obtained
during each of two sessions. All pitch matches are shown in Table
1, with the across-subjects means of the pitch matches displayed in
the bottom row of the table. Paired t-tests were calculated to evaluate
if there were significant differences across sessions between the mean
pitch matches for each procedure. The t-tests revealed that the means of
the Binary procedure did not differ significantly (p=0.2952), while
the means of the Octave procedure were significantly different
(p=0.0198). Thus, for the group of subjects, the mean pitch matches
between Sessions 1 and 2 were significantly different only for the
Octave procedure.

Table 1.Tinnitus pitch matches for each subject.

Pitch match (Hz)

Binary procedure

Octave procedure

Subject

Session 1

Session 2

Session 1

Session 2

1

620

3180

1000

2520

2

5040

6340

4000

6340

3

1580

2520

1580

620

4

2000

800

2000

500

5

3180

3180

3180

6340

6

2520

5040

2520

5040

7

5040

6340

8000

3180

8

8000

10080

6340

10080

9

12700

16000

10080

16000

10

5040

8000

6340

8000

11

6340

500

500

500

12

4000

12700

1000

4000

13

16000

16000

16000

16000

14

10080

5040

10080

10080

15

5040

5040

3180

4000

16

12700

12700

2000

12700

17

6340

5040

1260

12700

18

6340

8000

8000

8000

19

8000

6340

2520

1260

20

620

3180

500

10080

Mean

6059

6801

4504

6898

To evaluate within-subject reliability of responses, differences
were calculated between individual Session 1 and Session 2 pitch matches
for each procedure (Table 2). For the Binary procedure, the
Session 1 pitch match was subtracted from the Session 2 pitch match, and
the mean of these differences was 742 Hz. When the same calculations
were made for the Octave procedure, the mean of the differences was 2394
Hz. Thus, for both procedures, there appeared to be a trend for pitch
matches to be higher in frequency during the second session.

Table 2.Individual differences in pitch matches between sessions.

Pitch match difference (Hz),Session 2 minus Session 1

Subject

Binary

Octave

1

2560

1520

2

1300

2340

3

940

-960

4

-1200

-1500

5

0

3160

6

2520

2520

7

1300

-4820

8

2080

3740

9

3300

5920

10

2960

1660

11

-5840

0

12

8700

3000

13

0

0

14

-5040

0

15

0

820

16

0

10700

17

-1300

11440

18

1660

0

19

-1660

-1260

20

2560

9580

Mean

742

2394

The directionality of the individual differences, however, was
random between subjects; thus, the trend was not significant. To
determine the magnitude of these differences, disregarding
directionality, the absolute values of the differences were calculated
(Table 3). The means of the absolute values of the differences
were 2246 Hz for the Binary procedure, and 3247 Hz for the Octave
procedure. Thus, the magnitude of the differences was, on average,
larger for the Octave procedure, but the difference between the two
means was not significant (paired t-test, p=0.3282).

Pearson product-moment correlation coefficients were calculated
between the Session 1 and Session 2 pitch matches for each procedure.
The Pearson r was 0.757 (p<0.0001) for the Binary procedure, and 0.589
(p=0.0053) for the Octave procedure.

To provide an overall perspective of response reliability for both
procedures, distributions of the between-sessions pitch match
differences are shown in Figure 2. For this analysis, the test
frequencies, in Hz, were converted to their frequency position
in ascending order so that differences between frequencies would be
spaced logarithmically, roughly equivalent to their relative spacing on
the basilar membrane. The shapes of the distributions can be described
by their coefficients of skewness and kurtosis. Skewness was -0.807
and 0.597, and kurtosis was 2.267 and 0.161 for the Binary and Octave
procedures, respectively. Thus, the distribution of the differences with
the Binary procedure was negatively skewed, indicating that the negative
differences (reflecting pitch matches becoming higher in frequency
during Session 2) were greater than the positive differences (pitch
matches becoming lower in frequency).

Figure 2. Distributions of differences in pitch matches between sessions. For this
analysis, each test frequency was coded as a "frequency position,"
i.e., position 1 represents 500 Hz, position 2 represents 820 Hz,
et cetera.

In contrast, the distribution for the Octave procedure was
positively skewed. The kurtosis values are scaled so that a value of
zero indicates a normal distribution. The distribution for the Binary
differences was more positively peaked than normal (indicating more data
in the central part of the distribution), while the Octave differences
were more normally distributed.

Reliability of the responses can also be depicted as confidence
intervals. Table 4 shows confidence intervals with the
percentages of the numbers of differences falling within each specified
interval. For example, 30 percent of the inter-session differences were
within (plus or minus) one-third octave for the Binary procedure (20
percent for the Octave procedure). Seventy percent of the differences
were within one octave for the Binary procedure (50 percent for Octave).

Testing time was recorded for each procedure. The Octave procedure
required an average of 24 min and 20 min for Sessions 1 and 2, respectively.
The Binary procedure required an average of 24 min and 25 min, respectively.

DISCUSSION

This study follows a previous investigation that demonstrated
repeatable tinnitus pitch matches using our computer-automated system
(6). The previous and present investigations each used adaptations of
the manual tinnitus-matching procedure that has received extensive use
at the Oregon Tinnitus Clinic (13,14). In the previous study, the
computer-automated protocol was designed to replicate the testing
procedure used with the manual method. The starting test frequency was 1
kHz, and testing proceeded in ascending 1-kHz frequency steps to
approach gradually the frequency of a tone that most closely matched the
perceived tinnitus frequency of the patient. Such a procedure can be
tedious to arrive at a pitch match that most often occurs in the 4-8
kHz frequency range (15-17). Testing in the previous study required up
to 79 min, which would not be too unexpected for a slow responder with a
very high tinnitus frequency.

To increase the speed of arriving at a pitch match, two new
pitch-match procedures were evaluated in the present study. With the
"Octave" procedure, matching tones started at 1 kHz, but then
progressed in octave intervals to bracket the tinnitus pitch. The
"Binary" procedure started at a middle audiometric frequency (3.18
kHz), and the order of frequencies was designed to bracket the tinnitus
pitch to within a quartile of the test-frequency range. Results of this
study revealed that the Binary procedure generally provided more
reliable between-session pitch matches than the Octave procedure.
Collapsing across both sessions, the overall average time to obtain a
pitch match with the Octave procedure was 25 min, and 22 min for the
Binary procedure. Clinically, this time difference would not be
considered significant.

Individual Differences in Pitch-matching Ability
Matching the pitch of tinnitus might appear to be a straightforward
task that should be accomplished easily. Studies that have obtained
repeated pitch matches, however, have shown that it is extremely
difficult to obtain good reliability of responses (5). In general, pitch
matches for tinnitus are not as reliable as loudness matches, and
individuals vary greatly in their ability to match their tinnitus pitch.
There can be large differences between "musical" versus "non-musical" subjects in their initial ability to make frequency
discriminations (18). Thus, individuals with musical training or who
work in acoustics generally have more natural pitch matching ability,
while naive listeners can have difficulty differentiating the
higher pitched of two tones (19). For those who are untrained, however,
their inability can improve with practice, and even supposedly "tone
deaf" individuals can perform good frequency discrimination with enough
practice.

New patients are also likely to be unfamiliar with tinnitus
evaluation techniques and terminology, which could cause them to respond
inappropriately, especially during the initial phases of the automated
program. In particular, if patients confuse the terms "loudness" and
"pitch," they will not be capable of performing tinnitus loudness and
pitch matching (14). Because of the practice effect for some
individuals, and the potential confusion regarding testing terminology,
it is critical to provide tinnitus patients with tone discrimination
practice before conducting tinnitus matching.

To address this concern, a pre-testing procedure, shown in the
Appendix, was developed and implemented for this investigation. The
protocol tested the ability of a subject to differentiate between
"louder" and "softer" tones, and between "higher" and
"lower pitched" tones. If the subject had difficulty making these
discriminations, the protocol also provided a minimum of training.

The pre-testing protocol was conducted just before each subject's
first evaluation with the automated system. Every subject was able to
respond correctly to the pre-testing tasks, and most subjects responded
correctly the first time each task was presented. Only a few had
difficulty, and upon re-instruction, were able to perform the tasks with
accuracy. The pre-testing protocol confirmed that patients understood
the difference between pitch and loudness, and that they could
differentiate higher pitched tones from lower pitched tones, and louder
tones from softer tones. This is important when performing tinnitus
matching because accurate responding requires an understanding of these
concepts. We are currently developing the pre-testing as an automated
program that will be presented by computer before testing with the
automated technique.

There is the further concern of patients with significant hearing
loss who may have reduced frequency-resolving ability. Clearly, such
individuals may be limited in their ability to make reliable frequency
judgments about their tinnitus pitch, even with training. Anecdotally,
we have encountered patients for whom all frequencies above a certain
value (e.g., 3 kHz) sound similar. It will therefore be necessary in the
future to devise a means of determining at which frequencies a patient
can make frequency discriminations, and to limit testing to those
frequencies.

Tinnitus Pitch-match Reliability
Obtaining reliable tinnitus pitch matches has been a vexing problem
for decades (5). The majority of these studies have reported
between-sessions pitch matches that were highly variable, and only one
study has documented reliable pitch matches within sessions (20). These
historically consistent findings raise the concern that if studies
report tinnitus pitch matches without repeated measurements, the
accuracy of the single measurements must be questioned.

According to questionnaire responses from a large population of
tinnitus patients, the sound quality of tinnitus varied for about
one-third of the patients (21). Variations over time, concerning pitch,
timbre, or loudness of tinnitus, thus present additional sources of
unreliability. Some patients describe multiple tinnitus sounds of which
one of the sounds must be identified as the predominant sound for tone
matching. Such individuals may have difficulty "remembering" their
predominant tinnitus sound for repeated tone matching.

Patients with tinnitus that varies, or that has multiple components,
will present the greatest challenges in obtaining reliable matches. If
the tone matches show variability, that variability must reflect a true
change in the patient's perception of their tinnitus. A tool that could
actually reflect such perceptual changes would be invaluable for a range
of clinical and research purposes (2). However, current methods of
tinnitus assessment have not reached the level of achieving reliable
pitch matches, even when the patient's tinnitus does not fluctuate.
Therefore, the first step in developing a reliable pitch match procedure
will require documentation of reliability with patients who have stable
tinnitus. The technique could then be used to measure actual tinnitus
fluctuations.

CONCLUSION

A tinnitus pitch-match is an important clinical measurement for:
quantifying a patient's tinnitus perception; specifying a therapeutic
masking noise that is centered around the tinnitus frequency; and,
enabling detection of changes that may occur during treatment (2,5,6,22). Obtaining accurate pitch matches is also important for clinical
research purposes. If the pitch match is not repeatable, then the
measurement is not valid for any of these applications. Therefore, the
pitch match experiments in the present study were directed at developing
a standardized clinical method for obtaining such measurements reliably.

Most previous tinnitus pitch-match protocols have relied on an
upward progression of test frequencies to approach the tinnitus
frequency gradually. This can be a tedious process, and, thus far,
reliability of pitch matches obtained with such methodology has not been
demonstrated. The present experiment was designed to shorten testing
time by using larger steps to bracket initially the tinnitus frequency
to a specific range. Smaller frequency steps were then used within the
identified range to determine the more precise tinnitus frequency.
Results of this testing provided further validation that computer
automation can be an efficient means of performing tinnitus matching.

Although this methodology has shortened testing time considerably
from our previous investigation (6), further work is needed to design
protocols that can be conducted even more rapidly. Also, there is need
for further improvement in pitch match reliability for this technique to
offer utility for routine clinical application. Table 4 shows
confidence intervals for the inter-session differences with each method.
For the Binary and Octave procedures, respectively, 70 percent and 50
percent of the inter-session differences in pitch matches occurred
within one octave. A reasonable goal would be to achieve approximately
95 percent of inter-session differences within one octave. Refinement
efforts will, therefore, target shorter testing time and improved
reliability of responses. Accomplishment of these goals could result in
standardization of tinnitus evaluation techniques that would ultimately
improve hearing health care services.